1. Introduction
Infectious bronchitis virus (IBV) is a Gammacoronavirus that
causes a highly contagious disease in chickens. The virus causes
severe economic losses to the poultry industry worldwide because
it canaffectthe upper respiratory and reproductive tracts, and some
strains can cause nephritis in chickens [1]. It is well known that the
primary problem in the control of infectious bronchitis is the ability
of the virus to generate antigenic diversity by inaccuracy of the
coronavirus RNA-dependent RNA polymerase and high frequency
of homologous RNA recombination [2,3]. Many studies have shown
that the degree of cross-protection tends to decrease among IBV
serotypes and genotypes [4,5].
Despite intensive vaccination efforts using attenuated live and
killed vaccines to prevent the disease, the emergence of new variant
strains that do not serologically cross-react complicates disease
∗ Corresponding author. Tel.: +82 2 450 3712; fax: +82 2 455 3712.
E-mail address: songcs@konkuk.ac.kr (C.-S. Song).
control and is an argumentfor vaccinating chickens with the type of
IBV causing the disease [3,6]. However, producing a live IBV vaccine
requires lengthy strategies that are time, cost, and labor intensive.
Attenuation of IBV by multiple passages (over 100) in embryonated
eggs can delay a new vaccine’s clinical availability for several years.
This drawback is compounded by the time required for verification
of the vaccine to obtain licensing, as well as the current lack of
available cell lines for vaccine production, which could accelerate
vaccine production. Furthermore, there is no guarantee that the
viral strain used to produce the vaccine will still be endemic at the
time of vaccination [7–9].
Our previous study revealed that the QXIBV strain originating
from China has been introduced in Korea and has formed a
new cluster in the field [10]. This new cluster, represented by
the K40/09 strain, is a natural recombinant strain between the
Korean nephropathogenic strain KM91 and the QXIBV strain. In
a previous challenge study, we characterized the Korean variant
IBV K40/09 strain with regard to its immunogenicity and crossprotective
efficacy against heterotype strains and its potential as a
vaccine candidate [11].
http://dx.doi.org/10.1016/j.vaccine.2015.07.043
0264-410X/© 2015 Elsevier Ltd. All rights reserved.
T.-H. Lim et al. / Vaccine 33 (2015) 7370–7374 7371
The development of a temperature-adapted vaccine has been
attempted to increase safety and shorten the time of attenuation
in several studies [12–14]. However, our experience shows that,
besides desirable levels of attenuation and immunogenicity, other
traits such as good growth properties should also be considered
for live vaccine strains, and that this attenuation process may not
work for all viruses. In the present study, we evaluated the safety
and cross-protective efficacy of heat-adapted, live attenuated IBV
derived from the K40/09 strain. The results of the present study
might provide information for future IBV vaccine development and
vaccination strategies.